There have been devised air conditioners adapted to perform cooling, heating, or air-conditioning by utilizing exhaust heat from various heat-producing apparatuses, equipment, and facilities. Among such air conditioners which inventors of the invention devised, an air conditioner for performing at least cooling is devised in such a way as to include an absorption chiller of what is called the heat transfer medium drive type, which is adapted to recover exhaust heat and driven by a heat transfer medium, and as to perform cooling by supplying an indoor unit with a refrigerant cooled by the absorption chiller. Further, an air conditioner for performing at least heating is devised in such a way as to recover exhaust heat and as to perform heating by supplying an indoor unit with a heat transfer medium. Moreover, such air conditioners adapted to perform air-conditioning by utilizing exhaust heat are devised in such a manner as to have an auxiliary heating device for heating a heat transfer medium in a case, in which an amount of exhaust heat from an exhaust heat source is insufficient for performing cooling or heating, by utilizing heat of combustion in a burner or heat from a heater so as to make up for the shortage of heat, and also devised so that the temperature of the heat transfer medium is maintained in a predetermined range by controlling an operation of driving such an auxiliary heating device according to the temperature of the heat transfer medium so that the heat transfer medium always has a sufficient amount of heat.
Meanwhile, even in the case that the amount of exhaust heat is at a level insufficient for maintaining the temperature of the heat transfer medium within the predetermined range during a cooling operation, when the cooling load of the indoor unit is low, the absorption chiller sometimes can sufficiently cool the refrigerant and provide a cooled state by using only such an amount of exhaust heat. In such a case, the air conditioner, which is adapted to maintain the temperature of the heat transfer medium within the predetermined range by controlling the operation of driving the auxiliary heating device according to the temperature of the heating device, consumes energy by unnecessarily heating the heat transfer medium by means of the auxiliary heating device regardless of the cooling load. Therefore, even though the air conditioner is of the type utilizing exhaust heat, the energy-saving capability thereof is degraded.